Note: I always use a base weapon cartridge for the
calculations. This should be the normal FMJ (full metal jacket) version of the
bullet. Modifications for special ammunition types such as Armor Piercing,
Hollow Point, Tracer, etc are handled separately.

Damage Conversion

Since the most basic element of damage is how big a hole you
punch in something, base damage is determined by the diameter (caliber) of the
weapon according to the following chart:

Damage

Caliber

Metric

DC

Damage

0.5

1.27mm

4

1d6+1K

0.1

2.54mm

5

1
1/2d6K

0.15

3.81mm

5.5

2d6-1K

0.2

5.08mm

6

2d6K

0.3

7.62mm

7

2d6+1K

0.4

10.16mm

8

2
1/2d6K

0.45

11.43mm

8.5

3d6-1K

0.5

12.7mm

9

3d6K

0.71

18mm

10

3d6+1K

Example: The 45 ACP has an actual diameter of .452 inches.
This results in a base damage of 3d6-1 RKA

The chart can use either inches (Caliber) or metric measures
for the lookup. Damage is given in both Damage Classes (DC) and actual RKA
values.

A note on the half DC values (5.5 and 8.5): In Hero System
3d6-1 and 2 1/2d6 are equal in active point cost despite the fact that 3d6-1 has
a slight edge in final result. The 5.5 and 8.5 values take this into account by
displaying the small but significant difference where they are used.

The most basic measure of penetration is determined by the mass of the penetrating
object divided by it's impact area (call Sectional Density in ballistics) multiplied
by its velocity. This conversion makes use of the Armor
Effect house rules and the Piercing rules from 5th edition Dark Champions
supplement to Hero.

Relative penetration ability can be expressed as:

Mass (in grains) / 7000 / (bullet diameter) ^ 2 *
Velocity)

The result is referenced on the following chart to determine
the Hero System Effect:

Penetration

Penetration

Armor
Effect

0

x3

100

x2

150

x1.5

200

x1.25

450

Normal

550

-1

704

-2

940

-3

1304

-4

1863

-5

Example: The .45 ACP bullet has a Mass of
230 grains, diameter of .452 inches and velocity of 850 fps. The Penetration
value is 230/7000/.452^2*850 or 136 resulting in an Armor Resistance of x2.

So far, the .45 ACP damage would be
expressed as 3d6-1 RKA, Armor x2.

For Penetration values of less than 450, the effect is an multiple
of the armor value. For values of 600 and higher, the effect is a reduction of
the armor by the listed value as per the Piercing power.

Thus a flak Vest with 5 points of resistant defense would
give 10 points of armor against a Penetration 100 weapon, but only 1 point
against a penetration 950 weapon.

These value has the least real world backing as it's related
to the old concept of 'knockdown power' which has been debated and argued for
generations without a good resolution.

At its most basic level, there is little doubt that hitting
someone with something bigger, heavier and faster produces a better result. To
this end, let's use Hatcher's Formula developed in the first half of the 20th
century as a measure of 'knockdown power' to determine the Stun Modifier.

Weapon Handling

This value in HERO is the STR required to properly handle a weapon. Like most
things, a great many factors weigh into this single concept. Shape and design of
the weapon, build of the shooter, even air temperature and altitude. Luckily for
us much of this would fall between the limited number of values HERO provides.
Even so, we're going to have to simplify greatly and ignore important
considerations just to be able to produce a single value that applies to all
characters without exception.

Towards that end, we'll focus on a simplified model- that of Free
Recoil Energy. Even here, we'll take huge steps of simplification- assuming for
example that gas pressure is constant for all weapons (not true in the least of
course, we're using the standard value for 30-06 style rifles). Also simplified
is the effect of barrel length for which we'll assume that gas pressure is in
direct nearly proportion to barrel length (to which we'll add a vastly
simplified 10" in order to prevent
division by zero error as well as fudging the initial pressure build and the
effect of progressive powders). The final number will be a simple measure of
Recoil- lacking in many ways, but at least capable of providing us with a result
that doesn't require massive research for each individual weapon. Those
interested in a full treatment of Recoil are advised to consult Hatcher's
Notebook (ISBN 0-8117-0795-4) one of the definitive works on firearms.

The simplified Formula (with various constants left intact) are as follows:

Recoil Impulse (RI) = (bm+(1.75*30/(bl+10))*cm)*15.3*v/(7000*gm*2.2)

Recoil Energy =
RI^2*1/2*gm*2.2/32.16

bm
Bullet mass in grams

bl
Barrel Length

cm
Powder mass in grams if smokeless (divide by four as rule of thumb for black
poweder)

v
Muzzle Velocity

gm
Mass of unloaded Weapon in kg (determining recoil for the last shot, or worst
case)

1.75 Constant for
30-06 rifle gas pressures

Once one has determined the Recoil
Energy, consult the following chart to determine the base STR Min.

STR
Min

Recoil
Energy

STR
Min

0.00

1

1.00

1

1.25

2

1.55

3

1.93

4

2.41

5

3.00

6

3.74

7

4.66

8

5.80

9

7.22

10

9.00

11

11.21

12

13.97

13

17.40

14

21.67

15

27.00

16

33.63

17

41.90

18

52.20

19

65.02

20

81.00

21

100.90

22

125.70

23

156.59

24

195.07

25

Hands

STR Min

1

+3

1 1/2

+2

2

+0

Example: The M1911A1 pistol has a unloaded mass of 1.106, a bullet has a Mass of
15 grams, a powder mass of .33 grams, a barrel length of 5", and velocity of 850 fps.
It is also a 1 handed weapon..

RI =
(15+(1.75*30/(5+10))*.33)*15.3*850/(7000*1.106*2.2) = 12

Recoil Energy =
12^2*1/2*1.106*2.2/32.16 = 5.5

Thus the STR Min for the M1911A1 would be 8
+ 3 = 11

STR Min Weight Modifier

Very heavy weapons can be unwieldy in their own right requiring a fair amount
of STR just to aim and move. It's very common for such weapons to include
bipods, tripods, and even heavier carriage mounts in a few cases to offset their
mass.

These values represent how concealable the weapon is (PER Mod) and how easily
it's used in close quarter combat (page 193 of 5th Edition Dark Champions).
We'll simplify by basing these values on the overall weapon length as per the
following chart.

Weapon
Size

Overall
Length

PER
Mod

CQB
Mod

0

+0

+0

5

+1

+0

7.5

+2

+0

9

+3

+0

12

+4

-1

21

+5

-1

30

+6

-2

39

+7

-3

48

+8

-4

Example: The M1911A1 pistol has overall length of 8.62 inches
give us a PER Mode of +2 and CQB mod of +0.

The Range Modifiers (bonus to offset Range Modifiers) are based off barrel
length as per the following chart.

While in reality a large number of other factors would apply, to keep things manageable
we'll consider only two. Bolt Action rifles by nature tend to be more accurate
gaining an additional +1 modifier to the table results. Tube feed weapons
(typically lever action guns from the 'western' period) on the other other hand
tend to have more problems over range than other types of rifles and as such
take a -1 to the table results.

Range
Modifier

Barrel
Length

RMod

<4"

-1

4"

+0

7.5"

+1

12"

+2

19.5"

+3

24"

+4

Example: The M1911A1 is a semi-automatic pistol
(neither bolt action or tube) with a barrel Length of 5". It has a RMod of
+0

This represents the most important element of handling, just how difficult or
easy is it to hit with this weapon period. This is the most subjective of the
values and as such should be determined by the GM for the individual weapon.

For myself, I tend to give a +1 OCV for single action weapons of fine
quality. Exceptionally well made double action weapons (the Colt Python is a
good example) may also be deserving of the bonus.

Two handed weapons are generally given a +1 OCV unless the individual design
points out an exception. The AK-47 for example is a very reliable weapon, due in
large part to very loose fitting parts- a factor that makes accuracy with the
weapon something of fluke. As a result the AK-47 is left without the +1 OCV
modifier.

Example: The M1911A1 is single-action automatic
known for exceptional handing and accuracy. It's given +1 OCV

Final Result

How Realistic is the result?

The short answer?

Not very.

Just to pick on one of the values above, Hatcher's Formula was meant only to give a ballpark figure
and certainly wasn't designed to be used for rifle velocity weapons. In
addition, it was a combined value covering penetration and damage and not just a
'Stun Modifier'.

As the tumbling example in the theory
article shows, the effect of a weapon
is very dependent upon factors not even considered in these house rules- range,
bullet construction, target makeup, etc. All left out in the name of
simplification. One can min-max the above in silly ways rather easily (thus one should confine
conversions to real world weapons) and it's still after all this work a grainy system.

Lastly, the break points in the above charts were selected
more with an eye towards creating in game differences between major cartridges
than consideration of their actual relationship to real world damage. The
relative differences are present, but that's about all one can say about the
actual game values.

Even so, the basic concepts I needed are achieved. The
results of firearms are now closer to real world expectations and without a
complete overhaul of the system. Weapons are better defined and useable in
genres ranging from gritty street campaigns to four color comics. Only the most fanatic
gun freaks have room to complain.